linux-kernel - [RFC][PATCH 06/13] sched/fair: Export newidle

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Message-Id: <20190726161357.696559863@infradead.org>
Date:   Fri, 26 Jul 2019 16:54:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, juri.lelli@...hat.com
Cc:     linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        luca.abeni@...tannapisa.it, bristot@...hat.com,
        balsini@...roid.com, dvyukov@...gle.com, tglx@...utronix.de,
        vpillai@...italocean.com, rostedt@...dmis.org, peterz@...radead.org
Subject: [RFC][PATCH 06/13] sched/fair: Export newidle_balance()

For pick_next_task_fair() it is the newidle balance that requires
dropping the rq->lock; provided we do put_prev_task() early, we can
also detect the condition for doing newidle early.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c  |   18 ++++++++----------
 kernel/sched/sched.h |    4 ++++
 2 files changed, 12 insertions(+), 10 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3635,8 +3635,6 @@ static inline unsigned long cfs_rq_load_
 	return cfs_rq->avg.load_avg;
 }
 
-static int idle_balance(struct rq *this_rq, struct rq_flags *rf);
-
 static inline unsigned long task_util(struct task_struct *p)
 {
 	return READ_ONCE(p->se.avg.util_avg);
@@ -6848,11 +6846,10 @@ done: __maybe_unused;
 	return p;
 
 idle:
-	update_misfit_status(NULL, rq);
-	new_tasks = idle_balance(rq, rf);
+	new_tasks = newidle_balance(rq, rf);
 
 	/*
-	 * Because idle_balance() releases (and re-acquires) rq->lock, it is
+	 * Because newidle_balance() releases (and re-acquires) rq->lock, it is
 	 * possible for any higher priority task to appear. In that case we
 	 * must re-start the pick_next_entity() loop.
 	 */
@@ -9016,10 +9013,10 @@ static int load_balance(int this_cpu, st
 	ld_moved = 0;
 
 	/*
-	 * idle_balance() disregards balance intervals, so we could repeatedly
-	 * reach this code, which would lead to balance_interval skyrocketting
-	 * in a short amount of time. Skip the balance_interval increase logic
-	 * to avoid that.
+	 * newidle_balance() disregards balance intervals, so we could
+	 * repeatedly reach this code, which would lead to balance_interval
+	 * skyrocketting in a short amount of time. Skip the balance_interval
+	 * increase logic to avoid that.
 	 */
 	if (env.idle == CPU_NEWLY_IDLE)
 		goto out;
@@ -9729,7 +9726,7 @@ static inline void nohz_newidle_balance(
  * idle_balance is called by schedule() if this_cpu is about to become
  * idle. Attempts to pull tasks from other CPUs.
  */
-static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
+int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 {
 	unsigned long next_balance = jiffies + HZ;
 	int this_cpu = this_rq->cpu;
@@ -9737,6 +9734,7 @@ static int idle_balance(struct rq *this_
 	int pulled_task = 0;
 	u64 curr_cost = 0;
 
+	update_misfit_status(NULL, this_rq);
 	/*
 	 * We must set idle_stamp _before_ calling idle_balance(), such that we
 	 * measure the duration of idle_balance() as idle time.
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1449,10 +1449,14 @@ static inline void unregister_sched_doma
 }
 #endif
 
+extern int newidle_balance(struct rq *this_rq, struct rq_flags *rf);
+
 #else
 
 static inline void sched_ttwu_pending(void) { }
 
+static inline int newidle_balance(struct rq *this_rq, struct rq_flags *rf) { return 0; }
+
 #endif /* CONFIG_SMP */
 
 #include "stats.h"